DOCSLIB.ORG

The Subslab Flow Field and Implications for Mantle Dynamics Maureen D

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Subslab Flow Field and Implications for Mantle Dynamics Maureen D JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 114, B10312, doi:10.1029/2008JB006200, 2009 Click Here for Full Article Mantle flow in subduction systems: The subslab flow field and implications for mantle dynamics Maureen D. Long1,2 and Paul G. Silver1,3 Received 6 November 2008; revised 8 June 2009; accepted 7 July 2009; published 28 October 2009. [1] The character of the mantle flow field in subduction zones remains poorly understood, despite its importance for our understanding of subduction dynamics. In particular, little attention has been paid to mantle flow beneath subducting slabs. In order to identify processes that make first-order contributions to the global pattern of subslab mantle flow, we have compiled shear wave splitting measurements from subduction zones worldwide from previously published studies and estimated average splitting parameters for the subslab region. Globally, the subslab region is overwhelmingly dominated by trench-parallel fast splitting directions. We tested for relationships between splitting delay time, a measure of the strength of anisotropy, and parameters that are indicators of tectonic processes, such as trench migration velocity, convergence velocity and obliquity, age of subducting lithosphere, and slab dip, curvature, seismicity, and thickness. We used several different plate motion models to describe plate and trench motions and evaluated the differences among the models. We find that only one parameter, namely, the trench migration velocity in a Pacific hot spot reference frame, appears to correlate well with the strength of the subslab splitting signal. This finding supports a model in which the mantle beneath subducting slabs is dominated by three-dimensional flow induced by trench migration. We explore several implications of our model for various aspects of mantle dynamics, including the choice of a suitable reference frame(s) for mantle flow, the existence of a thin decoupling zone between slabs and the subslab mantle, and consequences for mass transfer between the upper and lower mantle. Citation: Long, M. D., and P. G. Silver (2009), Mantle flow in subduction systems: The subslab flow field and implications for mantle dynamics, J. Geophys. Res., 114, B10312, doi:10.1029/2008JB006200. 1. Introduction that drive it have implications for our understanding of the formation and migration of melt, volcanic production and [2] Subduction zones, where cold, negatively buoyant hazard, the tectonics of the fore-arc and back-arc region, lithosphere is recycled into the Earth’s mantle, represent and the style of mantle convection and mixing. In particular, both key components of the plate tectonic system and prime the characterization of mantle flow beneath downgoing sites of volcanic and seismological hazard [e.g., Stern, slabs, and the associated implications for how slabs interact 2002]. Subduction zones represent perhaps the most tecton- with surrounding mantle material, has received little atten- ically complicated regions on the Earth, and although much tion. In this study, we focus on anisotropy and mantle flow progress has been made in understanding their structure and in the subslab region, for several reasons. First, despite its dynamics, several crucial aspects of the subduction process importance for a complete understanding of the mantle flow remain enigmatic. In particular, the dynamic interaction field associated with subduction, the subslab region has between sinking slabs and the surrounding mantle flow been paid comparatively little attention in studies of mantle field remains poorly understood. The simplest model for flow in subduction systems, in contrast to the mantle wedge. this flow field invokes two-dimensional flow, with corner Second, as discussed later in this paper, the relationship flow in the mantle wedge above the slab and entrained flow between seismic anisotropy and mantle flow is much more beneath it; however, this model is increasingly contradicted straightforward for the subslab region than for the wedge, by seismological (and other) observations. The character of where unusual olivine fabrics [Jung and Karato, 2001] or the subduction zone flow field and the nature of the forces effects from melt [Holtzman et al., 2003] are possible and the interpretation of seismic anisotropy can be more am- 1Department of Terrestrial Magnetism, Carnegie Institution of biguous. Third, as we will show, observations of anisotropy Washington, Washington, D. C., USA. in the subslab region are much simpler and exhibit much 2Now at Department of Geology and Geophysics, Yale University, New Haven, Connecticut, USA. less regional variation than do comparable observations for 3Deceased 7 August 2009. the wedge region. [3] The most direct constraints on the geometry of mantle Copyright 2009 by the American Geophysical Union. flow are obtained through observations of seismic anisot- 0148-0227/09/2008JB006200$09.00 ropy. In particular, the observation that seismic shear waves B10312 1of25 B10312 LONG AND SILVER: SUBDUCTION ZONE MANTLE FLOW B10312 successfully explains many aspects of global subduction zone splitting patterns. This model, in which the subduction zone flow field is controlled by 3-D flow induced by the migration of the trench with respect to the underlying mantle, explains the preponderance of trench-parallel fast directions beneath the slab as well as the observed correla- tion between trench migration velocity and delay times for both the subslab and wedge regions that we observed in a global compilation of splitting measurements. [6] Here, we expand our previous work and present a more complete investigation of the relationships between splitting parameters and parameters that describe the sub- duction process, with a focus on the subslab mantle flow Figure 1. Sketch of various raypaths involved in isolating field. The work presented here extends our previous inves- slab versus subslab anisotropy, including local S phases tigation in four ways. First, we have augmented our global from slab earthquakes (white stars), teleseismic SKS-type database of subduction zone splitting measurements with phases measured at stations (black squares) above the slab, characterizations of source-side anisotropy from teleseismic and direct S from slab earthquakes measured at teleseismic measurements of intermediate-depth earthquakes occurring distances. in subduction zones [e.g., Wookey et al., 2005; Rokosky et al., 2006; Mu¨ller et al., 2008]. These data provide a more are birefringent, and undergo ‘‘splitting’’ as they propagate direct constraint on anisotropy and flow beneath downgoing through anisotropic regions of the Earth, has provided a tool slabs, as the measurements are uncontaminated by anisotropy for studying the local geometry of mantle flow beneath in the wedge. Second, we present comparisons between seismic stations (see overviews by Silver [1996], Savage subslab splitting parameters and a wide variety of parame- [1999], and Park and Levin [2002]). Shear wave splitting ters that describe subduction, such as trench migration studies, which measure the fast direction f and the delay velocity, convergence velocity and obliquity, age and spread- time dt for each shear arrival, have increased in popularity ing history of subducting lithosphere, slab dip, curvature, and now represent a standard tool for probing mantle seismicity, thickness, and morphology, and arc length. deformation. Subduction zones have been a popular target These comparisons allow us to test alternative hypotheses for shear wave splitting practitioners, and since early studies concerning factors that control anisotropy beneath the by Ando et al. [1983], Fukao [1984], and Bowman and mantle wedge. Third, we revisit the comparisons between Ando [1987], several dozen splitting studies in subduction subslab split times and trench migration velocities shown by zone regions have been performed. With the wealth of such Long and Silver [2008] using a variety of global reference data now available, it is both important and timely to frames and plate motion models [Schellart et al., 2008; undertake comprehensive studies of shear wave splitting Lallemand et al., 2008]; in principle, this should allow for behavior in subduction zones globally, with the aim of the identification of an ideal ‘‘rest frame’’ for the convecting determining the dominant properties of the mantle flow mantle, at least in the Pacific, around which most subduc- field associated with the subduction process. tion zones in our compilation are located. Finally, we [4] Although shear wave splitting in subduction zone address in detail some of the implications of the Long and regions has been extensively characterized, consensus on Silver [2008] model for mantle dynamics, including the how it relates to mantle processes has not been forthcoming, nature of a likely decoupling zone beneath subducting slabs for several reasons. First, the inherent structural complexity and constraints on mass exchange between the upper and of subduction zones (which comprise the overriding plate, lower mantle. the superslab mantle wedge, the slab itself, and the subslab mantle) not only makes the interpretation of splitting 2. A Global Data Set of Subslab Shear Wave measurements difficult, but it makes the measurements Splitting Parameters in Subduction Zones themselves challenging; complex anisotropic structure 2.1. Methods for Isolating the Subwedge Contributions beneath a station leads to complicated splitting patterns which exhibit significant variations [e.g.,
Load more

Recommended publications
  • Low-Frequency Tremor and Slow Slip Around the Probable Source Region
    Proceeding of the UJNR 5th Earthquake Research Panel Meeting, 2004 1 Low-frequency tremor and slow slip around the probable source region of the Tokai Earthquake { A new indicator for the Tokai Earthquake prediction provided by unified seismic networks in Japan { Noriko Kamaya (Seismological and Volcanological Department, JMA), Akio Katsumata (Meteorological College, JMA) and Yuzo Ishigaki ( Seismological and Volcanological Department, JMA) Abstract Enhancement of seismic networks in the Japan Islands of these years revealed occurrence of deep low-frequency continuous tremors of a belt distribution in the southwest Japan, where the subducting Philippine Sea plate reaches depths of 25{40 km. The source region of the tremor is assumed to correspond to boundary region between oceanic and island crusts close to mantle wedge. The east end of the belt tremor distribution is adjacent to the probable source region of the Tokai Earthquake. A slow-slip event has continued in the west of the source region of the Tokai Earthquake since 2000. Synchronous activation of the tremor and slow-slip speed was observed in 2003. This suggests some relationship between the slow-slip and the tremor activity. We expect that the tremor activity could be a new valuable indicator for the Tokai Earthquake prediction. The long duration of the tremor indicates existence of fluid relating to its generation. The most probable fluid is considered to be water produced by dehydration of chlorite and formation of clinopyroxene in the oceanic crust on the basis of data from high pressure and temperature experiments. The northern border of the belt distribution is possibly rimmed by the edge of the mantle wedge because serpentine formation absorbs fluid water.
    [Show full text]
  • Constraints on the Moho in Japan and Kamchatka
    Tectonophysics 609 (2013) 184–201 Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto Review Article Constraints on the Moho in Japan and Kamchatka Takaya Iwasaki a, Vadim Levin b,⁎, Alex Nikulin b, Takashi Iidaka a a Earthquake Research Institute, University of Tokyo, Japan b Rutgers University, NJ, USA article info abstract Article history: This review collects and systematizes in one place a variety of results which offer constraints on the depth Received 1 July 2012 and the nature of the Moho beneath the Kamchatka peninsula and the islands of Japan. We also include stud- Received in revised form 12 November 2012 ies of the Izu–Bonin volcanic arc. All results have already been published separately in a variety of venues, and Accepted 22 November 2012 the primary goal of the present review is to describe them in the same language and in comparable terms. Available online 3 December 2012 For both regions we include studies using artificial and natural seismic sources, such as refraction and reflec- tion profiling, detection and interpretation of converted-mode body waves (receiver functions), surface wave Keywords: Kamchatka dispersion studies (in Kamchatka) and tomographic imaging (in Japan). The amount of work done in Japan is Japan significantly larger than in Kamchatka, and resulting constraints on the properties of the crust and the upper- Crustal structure most mantle are more detailed. Upper-mantle structure Japan and Kamchatka display a number of similarities in their crustal structure, most notably the average Moho crustal thickness in excess of 30 km (typical of continental regions), and the generally gradational nature of the crust–mantle transition where volcanic arcs are presently active.
    [Show full text]
  • ITM International Tectonics Meeting
    NUMO-TR-16-04 TOPAZ Project Long-term Tectonic Hazard to Geological Repositories Toward practical application of the ITM-TOPAZ methodology February 2017 Nuclear Waste Management Organization of Japan (NUMO) 2017 年 2 月 初版発行 本資料の全部または一部を複写・複製・転載する場合は，下記へ お問い合わせください。 〒108-0014 東京都港区芝 4 丁目 1 番地 23 号 三田 NN ビル 2 階 原子力発電環境整備機構 技術部 電話 03-6371-4004（技術部） FAX 03-6371-4102 Inquiries about copyright and reproduction should be addressed to: Science and Technology Department Nuclear Waste Management Organization of Japan Mita NN Bldg. 1-23, Shiba 4-chome, Minato-ku, Tokyo 108-0014 Japan ©原子力発電環境整備機構 (Nuclear Waste Management Organization of Japan) 2017 NUMO-TR-16-04 TOPAZ Project Long-term Tectonic Hazard to Geological Repositories Toward practical application of the ITM-TOPAZ methodology February 2017 Nuclear Waste Management Organization of Japan (NUMO) 各章の和文要約 1 序論 本報告書は，国際プロジェクトメンバーが作成した原稿を NUMO が編集したもの である。NUMO は，地層処分システムに著しい影響を及ぼす火山活動や断層活動な どの自然現象の発生可能性を確率論的に評価するための手法として，ITM 手法1を開 発した。続いて，プレート運動の安定性を必ずしも前提にできない超長期の評価に 向けて，ITM-TOPAZ 手法2の開発を進めた。東北地方および中国地方を対象とした ケーススタディを通じて，ITM-TOPAZ 手法の日本の地質環境への基本的な適用性を 確認してきた。今回，ITM-TOPAZ 手法の適用性のさらなる向上を目指し，再び東北 地方を対象に，火山活動・断層活動に加えて隆起・侵食の変遷に関するシナリオの 拡充，それらの影響の評価方法の高度化などを行った。 2 広域変遷シナリオ（RES: Regional Evolution Senarios）の拡充 これまでに例示した将来 100 万年までのプレート運動の変遷に関する四つのシナ リオ（RES1: 現在の傾向が継続，RES2: プレート収束速度が増加，RES3: プレート運 動の方向が変化，RES4: プレート収束速度が減少）における，東北地方の背弧域 （日本海側），脊梁山地，前弧域（太平洋側）での広域的な火山活動，断層活動， 隆起・侵食の傾向について，追加情報に基づき記述を補強した。さらに，最近の科 学的知見の進展を踏まえたシナリオの拡充の可能性について述べた。 3 サイト変遷シナリオ（SES: Site Evolution Senarios）の設定 背弧域（日本海側），脊梁山地，前弧域（太平洋側）を代表する数十
    [Show full text]
  • Evolution History of Gassan Volcano, Northeast Japan Arc
    Open Journal of Geology, 2018, 8, 647-661 http://www.scirp.org/journal/ojg ISSN Online: 2161-7589 ISSN Print: 2161-7570 Evolution History of Gassan Volcano, Northeast Japan Arc Ryo Oizumi1, Masao Ban2*, Naoyoshi Iwata2 1Graduate School of Science and Technology, Yamagata University, Yamagata, Japan 2Faculty of Science, Yamagata University, Yamagata, Japan How to cite this paper: Oizumi, R., Ban, Abstract M. and Iwata, N. (2018) Evolution History of Gassan Volcano, Northeast Japan Arc. Evolution history of the volcano is essential not only to characterize the vol- Open Journal of Geology, 8, 647-661. cano, but also consider magma genesis beneath the volcano. Most of the stra- https://doi.org/10.4236/ojg.2018.87038 tovolcanoes in northeast Japan follow a general evolutional course: cone building, horse-shoe shaped caldera forming collapse, and post-caldera stages. Received: June 4, 2018 However, the detailed history of each stage is not well investigated. We inves- Accepted: July 10, 2018 Published: July 13, 2018 tigated evolution history of young edifice of Gassan volcano, representative stratovolcano in rear side of northeast Japan arc. Most of the products are la- Copyright © 2018 by authors and vas, which are divided into two groups by geomorphologic and geologic fea- Scientific Research Publishing Inc. tures. The former (Gassan lower lavas) is composed of relatively thin and This work is licensed under the Creative Commons Attribution-NonCommercial fluidal lavas, whose original geomorphology remains a little, while the latter International License (CC BY-NC 4.0). (Gassan upper lavas) is composed of relatively thick and viscous lavas, whose http://creativecommons.org/licenses/by-nc/4.0/ original geomorphology is moderately preserved.
    [Show full text]
  • Workshop Reports on Bend-Fault Serpentinization (BFS) and Bend-Fault Hydrology in Old Incoming Plate (H-ODIN)
    Workshop reports on Bend-fault serpentinization (BFS) and Bend-Fault Hydrology in Old Incoming Plate (H-ODIN) 19-21 June, 2016, University of London, Royal Halloway Jason P. Morgan, Royal Holloway, University of London, UK Gou Fujie, JAMSTEC, Japan Ingo Grevemeyer, GEOMAR, Germany Tim Henstock, University of Southampton, UK Tomoaki Morishita – Kanazawa University, Japan Damon Teagle, University of Southampton, UK 1. Introduction and workshop goals Crustal hydration at mid-ocean ridges by hydrothermal circulation has been considered to be the first-order control on the degree of the oceanic plate hydration (see ‘Primary Hydration’ region on Fig. 1). Previous ocean drilling projects have aimed to reveal hydration processes and their extent of oceanic crust at spreading centers (e.g., Alt et al., 1996; Bach et al., 2003; Wilson et al., 2006). Recently, hydration due to plate bending-induced normal faults (bend-faults) in the region between the trench axis and outer rise (outer rise hereafter) has also drawn considerable attention (see ‘Rehydration’ region on Fig. 1). During the last decade, multiple independent geophysical structure studies have revealed that plate bending-induced normal faults in outer rise regions around the world are associated with significant hydration along (e.g., Grevemeyer et al., 2007; Ivandic et al., 2008; Key et al., 2012; Fujie et al., 2013). This bend-fault-linked hydration and Bend-Fault Serpentinization (BFS), with its associated physical and chemical changes is one of the most significant geological discoveries of the last 15 years. It has the potential to reshape our understanding of Earth’s deep water and carbon cycles, the ecology and evolution of species in deep-sea chemosynthetic environments, and even the fundamental mechanism by which slabs bend and unbend, thereby driving Plate Tectonics.
    [Show full text]
  • Threedimensional Seismic Velocity Structure and Configuration of The
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, B09315, doi:10.1029/2007JB005274, 2008 Three-dimensional seismic velocity structure and configuration of the Philippine Sea slab in southwestern Japan estimated by double-difference tomography Fuyuki Hirose,1 Junichi Nakajima,2 and Akira Hasegawa2 Received 18 July 2007; revised 23 June 2008; accepted 17 July 2008; published 26 September 2008. [1] Three-dimensional seismic velocity structure in and around the Philippine Sea plate subducting beneath southwestern (SW) Japan is determined by applying double- difference tomography method to arrival time data for earthquakes obtained by a dense nationwide seismic network in Japan. A region of low S wave velocity and high Vp/Vs of several kilometers in thickness is recognized immediately above the region of intraslab seismicity in a wide area from Tokai to Kyushu. This characteristic layer dips shallowly in the direction of slab subduction. Compared with the upper surface of the Philippine Sea slab based on seismic reflection and refraction surveys on seven survey lines, we interpret that the low-Vs and high-Vp/Vs layer corresponds to the oceanic crust of the Philippine Sea slab. On the basis of the position of the low-Vs and high-Vp/Vs layer and the precisely relocated hypocenter distribution of intraslab earthquakes, the upper surface of the Philippine Sea slab is reliably determined for the entire area of SW Japan. Nonvolcanic deep low-frequency earthquakes that occurred associated with the subduction of the Philippine Sea slab are distributed along the isodepth contour of 30 km in SW Japan, except for the Tokai district where the depth of deep low-frequency earthquakes becomes gradually deeper toward northeast.
    [Show full text]
  • Spatial Variations of Incoming Sediments at the Northeastern
    https://doi.org/10.1130/G46757.1 Manuscript received 14 July 2019 Revised manuscript received 4 February 2020 Manuscript accepted 10 February 2020 © 2020 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license. Published online 30 March 2020 Spatial variations of incoming sediments at the northeastern Japan arc and their implications for megathrust earthquakes Gou Fujie1, Shuichi Kodaira1, Yasuyuki Nakamura1, Jason P. Morgan2, Anke Dannowski3, Martin Thorwart4, Ingo Grevemeyer3 and Seiichi Miura1 1 Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama 236-0001, Japan 2 Department of Ocean Science and Engineering, Southern University of Science and Technology (SUSTech), Shenzhen 518055, China 3 GEOMAR–Helmholtz-Centre for Ocean Research Kiel, Kiel 24148, Germany 4 Institute of Geosciences, Christian-Albrechts University Kiel, Kiel 24118, Germany ABSTRACT subduction) show that the origin of smectite The nature of incoming sediments is a key controlling factor for the occurrence of megath- at the plate boundary fault is from pelagic red- rust earthquakes in subduction zones. In the 2011 Mw 9 Tohoku earthquake (offshore Japan), brown clay within the incoming sediments (Ka- smectite-rich clay minerals transported by the subducting oceanic plate played a critical role in meda et al., 2015; Moore et al., 2015). Thus, the development of giant interplate coseismic slip near the trench. Recently, we conducted inten- the composition of incoming sediments is also sive controlled-source seismic surveys at the northwestern part of the Pacific plate to investigate a key factor shaping the occurrence of mega- the nature of the incoming oceanic plate.
    [Show full text]
  • Spatiotemporal Variations in the Stress Field In
    Maeda et al. Earth, Planets and Space (2020) 72:117 https://doi.org/10.1186/s40623-020-01245-8 EXPRESS LETTER Open Access Spatiotemporal variations in the stress feld in the northeasternmost part of the NE Japan arc: constraints from microearthquakes Sumire Maeda1* , Toru Matsuzawa2 , Tomomi Okada2, Hiroshi Katao3, Takeyoshi Yoshida2 , Masahiro Kosuga4 and Makoto Otsubo1 Abstract We determined focal mechanism solutions of microearthquakes and examined the stress feld in the low-seismicity region from southern Hokkaido to eastern Aomori, NE Japan. The stress felds determined in this study comprise (1) a reverse faulting stress regime in southern Hokkaido with the axis of maximum compressional stress (σ1) being sub- horizontal and trending WNW–ESE, and (2) a stress regime in eastern Aomori to Tsugaru Strait that shows temporal variations and diferential stress of less than tens of MPa. The spatiotemporal variation in stress from eastern Aomori to Tsugaru Strait might refect the efects of the upper-plate bending and the 2011 Mw 9.0 Tohoku-Oki earthquake. It also indicates that the compressional stress caused by the descending Pacifc plate is relatively weak, which is similar to other areas in eastern parts of the NE Japan arc. Keywords: Focal mechanism, Stress feld, Low-seismicity area, Microseismicity, Forearc, Northeastern Japan, Pacifc plate subduction, Kurile arc Introduction in low-seismicity areas. However, to properly understand Te stress feld in inland areas of NE Japan is generally earthquake generation mechanisms, it is necessary to recognized as being associated with a WNW–ESE com- investigate the stress feld in low-seismicity areas as well pressional reverse-faulting stress regime (e.g., Townend as in areas with high seismicity.
    [Show full text]
  • Melting and Seismic Structure Beneath the Northeast Japan Arc
    GEOPHYSICAL RESEARCH LETTERS, VOL. 27, NO. 3, PAGES 425-428, FEBRUARY 1, 2000 Melting and seismic structure beneath the northeast Japan arc Hikaru Iwamori Geological Institute, University of Tokyo, Tokyo, Japan Dapeng Zhao Department of Earth Sciences, Ehime University, Matsuyama, Japan Abstract. Transportation of H20 associatedwith subduc- of the area [Zhao et al., 1992] (Fig.2). The NE Japan arc is tion of the Pacific plate beneath the northeast Japan arc one of the best test field of the model: (1) a denseseismic is modeled to predict distribution of aqueous solution and network with active seismicity have revealed the geometry melt, and the consequentP-wave velocity structure. The and velocity structures of the subducting Pacific plate, and observed velocity structure coincides well with the model the overlyingmantle wedge-crustsystem (e.g., [Zhao et al., for equilibrium transport of H20: most of H20 subductedis 1992, 1994]), (2) the geometricalrelationship between the brought down to 150-200 km depth along the slab, then the plate motion, trench and arc is simple, i.e., the Pacific plate aqueous fluid generated ascendsto initiate melting, which subducts nearly perpendicular to the Japan trench and the explainsthe low velocity regions(-•6% reduction) observed activevolcanic front (Fig.2), allowingus to apply the across- beneath the backarc, rather than beneath the volcanic front. arc 2-D modeling. Based on the comparison, we propose a If equilibrium transport of H20 occurs, initiation of melting model which accounts for the observations, including the beneath the backarcwith deep subductionof H20 is likely to regions with 6% reduction in P-wave velocity beneath the be the case also for other subduction zones with slabs older backarc, and discussthe fluid processesin subduction zones.
    [Show full text]
  • The Cause of the East–West Contraction of Northeast Japan
    Bulletin of the Geological Survey of Japan, vol. 68 (4), p. 155–161, 2017 Article The cause of the east–west contraction of Northeast Japan Masaki Takahashi1,* Masaki Takahashi (2017) The cause of the east–west contraction of Northeast Japan. Bull. Geol. Surv. Japan, vol. 68 (4), p. 155–161, 5 figs. Abstract: Northeast (NE) Japan, where the Pacific Plate is subducted to the west, frequently suffers large earthquakes not only along the Japan Trench but also along the Japan Sea side. Those occurred in the former area (subduction–zone earthquake) such as the 2011 off the Pacific coast of Tohoku Earthquake can easily be understood as a releasing process of accumulated stress along the boundary between the subducting Pacific Plate and the overlying plate. On the contrary, those in the latter area (inland earthquake), which occur at relatively shallow depth (<20 km), cannot be explained by such a simple dislocation model. Here I show, the cause of such inland earthquakes can be identified by considering the plate kinematics around the Japanese Islands on the basis of three dimensions, not conventional two dimensions, and the cause of the present E–W contractive tectonics of NE Japan is not the Pacific Plate motion itself but the northwestward–moving Philippine Sea Plate. Keywords: tectonics, Japanese Islands, inland earthquake, triple junction, Philippine Sea Plate, Pacific Plate 1. Introduction 40 million years (Harada and Hamano, 2000). Therefore, suppose the E–W contraction of NE Japan is caused by It is well known that the Japanese Islands are currently the Pacific Plate motion itself, the Japanese Islands should situated under E–W compression stress field (Terakawa have been contracted at least for 15 million years after and Matsu’ura, 2010).
    [Show full text]
  • Stress and Displacement Fields in the Northeastern Japan Island Arc As Evaluated with Three-Dimensional Finite Element Method and Their Tectonic Interpretations
    Stress and Displacement Fields in the Northeastern Japan Island Arc as Evaluated with Three-Dimensional Finite Element Method and Their Tectonic Interpretations 著者 Sato Kachishige 雑誌名 The science reports of the Tohoku University. Fifth series, Tohoku geophysical journal 巻 31 号 3-4 ページ 57-100 発行年 1988-06 URL http://hdl.handle.net/10097/45308 Tohoku Geophys. Journ. (Sci. Rep. TOhoku Univ., Ser. 5), Vol. 31, No. 3, 4, pp. 57-99, 1988 Stress and Displacement Fields in the Northeastern Japan Island Arc as Evaluated with Three- Dimensional Finite Element Method and Their Tectonic Interpretations KACHISHIGE SAT 0 International Latitude Observatory of Mizusawa, Mizusawa, Iwate Pref. 023 (Received March 25, 1988) Abstract : Numerical experiments for evaluation of the stress and displacement fields within the northeastern Japan island arc were performed by using three-dimensional finite element method. We study mainly the accumulation process of the stress within the arc by imposing boundary conditions as realistically as possible upon the plate-interaction models. Since this arc has very different structures in its southern and northern parts, calculations were separately made for these two parts. They roughly correspond to the Kanto and Tohoku districts, respectively. The patterns of calculated vertical displacement fields at the earth's surface are generally similar to the observed ones in the models of both parts. As to the stress, in the southern part, it is large not only in the shallower portion of the thrust zone between the subducting and overriding plates, but also in the deeper portion where two subducting slabs collide beneath the land area.
    [Show full text]
  • Ocean Drilling Program Initial Reports Volume
    Tamaki, K., Pisciotto, K., Allan, J., et al., 1990 Proceedings of the Ocean Drilling Program, Initial Reports, Vol. 127 1. BACKGROUND, OBJECTIVES, AND PRINCIPAL RESULTS, ODP LEG 127, JAPAN SEA1 Shipboard Scientific Party2 INTRODUCTION ized core-mantle interactions and heat transfer (Miyashiro, 1986); (2) convective flow induced in the asthenosphere by the sub- Leg 127 of the Ocean Drilling Program accomplished the ducting slab (Sleep and Toksöz, 1971; Andrews and Sleep, 1974; first successful penetration of the volcanic rocks which underlie Toksöz and Bird, 1977; Toksöz and Hsui, 1978); and (3) sea- the deep basins of the Japan Sea. The basaltic rocks recovered ward migration of the trench hinge line (Molnar and Atwater, at three of the four drilling sites provide valuable new con- 1978; Chase, 1978; Wu, 1978; Uyeda and Kanamori, 1979); re- straints on the style and timing of volcanism and, by inference, treat of the back-arc plate from the volcanic arc (Dewey, 1980); on the origin of these basinal areas (Fig. 1). In addition, this and intracontinental deformation such as the case of the Hima- drilling effort marks the first recovery of complete sedimentary layan convergence (Tapponier et al., 1982; Jolivet, 1986; Ki- sequences in this marginal sea. The vertical and lateral progres- mura and Tamaki, 1986; Lallemand and Jolivet, 1986). sions of the sedimentary facies within these sequences provide Within this context, no single process can easily account for the most updated view of how this marginal sea developed, the formation of all these western Pacific marginal basins. In from inception to the present day.
    [Show full text]